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Earth’s water
does not sit still. It changes form and moves from
place to place. |
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Water in the Air |
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Look around the room
you are in now. Can you see water
around you? Even if you do not see it, water surrounds you
all the time. This water is not in a liquid form as in rivers
or a solid form as in glaciers. This water is an invisible gas
called water vapor. Air always has some water vapor in it,
even in the driest deserts. This water vapor was liquid water
at some time in the past. It may have been water inside
a plant, in a tropical river, or in the Arctic Ocean. |
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Water vapor makes
up a very small fraction of the
gases in the air. The particles of water vapor, like
particles of other gases, are constantly moving.
Air pressure is the pressure of these gas particles
against another object. Air pressure pushes in
all directions because the gas particles move
in all directions. Air pressure decreases as
you move higher in the atmosphere. |
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The Water Cycle |
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on, through, and above Earth as it changes from one form to another
in the water cycle. The water cycle is the repeated movement of
water through the environment |
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in different
forms. The steps
of the water cycle include evaporation, condensation, precipitation,
and runoff.
These steps can be affected
by temperature, pressure,
wind, and the elevation of the
land. A simple water cycle is shown here. |
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